494 IMMUNITY 



toxin in the blood. Further investigation alone will settle these 

 and various other disputed points, and may remove many of the 

 apparent objections. At present we may say, however, that 

 Ehrlich's theory is the only one which even attempts to explain 

 the cardinal facts of this aspect of immunity. 



In connection with the condition of supersensitiveness referred to 

 above, an interesting phenomenon has recently been -described by 

 Theobald Smith, and is now generally known as "serum anaphylaxis," 

 or "Theobald Smith's phenomenon." It is briefly the following : If a 

 guinea-pig be injected with a quantity, say 5 c.c., of horse serum, no 

 disturbance follows ; if, however, the animal be previously treated, 

 say fourteen davs before, with a very small quantity of horse serum, 

 '001 c.c. (even less is sufficient), and then the 5 c.c. of serum be injected, 

 the animal usually dies within an hour with characteristic symptoms. 

 The general lesions are of hsemorrhagic nature, as pointed out by Gay and 

 Southard, 1 and occur especially in the stomach. The condition of super- 

 sensitiveness to the horse serum lasts fora long period of time. Accord- 

 ing to Gay and Southard the phenomenon depends upon a substance in 

 the horse serum which they call anaphylactin, and which persists for a 

 long period of time in the blood of the guinea-pig. This body they con- 

 sider to act as a slight irritant to the cells of the guinea-pig, and to 

 produce an increased affinity for the molecules in the horse serum. Ac- 

 cordingly when the second injection is made the rapid combination of these 

 substances with the cells result in the disturbances referred to. What- 

 ever may be the explanation, the phenomenon is of extreme importance 

 as showing the profound alterations in metabolism which may be induced 

 by a minute quantity of serum of a normal animal. 



The facts relating to hypersensitiveness raise the question of 

 whether in any immunisation procedure an injury may not be 

 constantly done to the cells forming the anti-substances. We 

 have already drawn attention to the occurrence of what Wright 

 has called the negative phase in the course of the increase of the 

 opsonic power of the serum aimed at in a bacterial vaccination. 

 There is evidence that such negative phases are common in all 

 immunisations. They have been also noted in the formation of 

 antitoxins, of immune-bodies, and of agglutinins. Thus in the case 

 of the first, Salamonsen and Madsen showed that the fall in the 

 content of an animal's serum in antitoxin after a fresh toxin injec- 

 tion was greater than could be accounted for by the neutralisa- 

 tion of the free antitoxin in the blood by the toxin introduced, 

 Iand they attributed the occurrence to an injury to the producing 1 

 cells temporarily diminishing the productive activity. The4 

 normal course of every immunisation may be said to consist in 

 a succession of positive and negative phases, and an effective 

 immunisation is one where each succeeding positive phase brings 



1 Vide Gay and Southard, Journ. Med. Research, xvi., 1907, 143. 



